1. Field of the Invention
The present invention relates to a method of finishing a concrete structure which comprises using a special aqueous acrylic acid ester resin emulsion to adhieve an imporved adhesive bond strength between the concrete structure and a finish layer.
2. Description of the Prior Art
In applying a cement-based finish layer such as cement motar to the bare surface of a concrete structure made of, say, concrete or lightweight concrete, attempts have been made to achieve an improved adhesive bond stength between the substrate surface and the cement-based finish layer by coating the substrate concrete surface with an aqueous synthetic resin emulsion adhesive beforehand and, after drying, applying a cement-based finishing material on top of the adhesive layer [Japanese Patent Publication Nos. 37832/1985 and 42828/1985]. The art described in the above patent publication No. 37832/1985 employs an aqueous emulsion of acrylic ester-styrene copolymer or ethylene-vinyl acetate copolymer as an adhesive agent with hopes of improving the antiquake adhesive bond strength but such adhesive does not provide a sufficient durability bond strength (weather-resisting bond strength) nor does it ensure a sufficient heat-resisting bond strength (bond strength at elevated temperature). Furthermore, in multi-layer coating (when a second or subsequent coat is further applied to a dried previous coat), marked reductions are encountered in the room temperature bond strength, heat-resisting bond strength and durability bond strength across the interface between the two coating lamellae.
In the method described in Japanese Patent Publication No. 42828/1985, a vinyl resin emulsion containing an epoxy resin component and an epoxy curing agent is used as an adhesive to improve the initial adhesive bond strength but since this adhesive composition has only a short pot life, it has the inconvenience that the two components must be mixed immediately before use. Moreover, it has the disadvantage that the bonding performance deteriorates with time after mixing. Furthermore, as the vinyl resin in the resin emulsion has no crosslinkable functional group within its molecule, it cannot provide a crosslinked structure, so that the composition does not provide a sufficient heat-resisting adhesive bond strength.
Aside from the foregoing methods comprising applying a cement-based finish layer onto the bare surface of a concrete structure, a method comprising laminating a high polymer sheet with the concrete surface of a substrate structure has been disclosed in Japanese Laid-Open Patent Application Kokai No. 129280/1984. In this method, an emulsion adhesive is coated on the concrete surface and before the resulting film dries, said high polymer sheet is superimposed so as to provide an integral unit. The emulsion adhesive used in this method is an acryl-crosslinkable emulsion adhesive such as a (meth)acryl ester-glycidyl methacrylate copolymer emulsion. This emulsion adhesive is characterized in that because the presence of a high polymer sheet on top of its layer, it attracts the alkali component of concrete composition from the concrete surface on account of its own moisture and is thereby crosslinked and cured to display an adhesive bond strength. Therefore, it has the advantage that the decrease in bond strength due to temperature increase is prevented. However, the above emulsion adhesive is so low in reactivity that when coated on the surface of alkali-lean foamed or autoclaved lightweight concrete (hereinafter referred to briefly as ALC) or an aged concrete structure whose surface has been neutralized, it does not undergo sufficient alkali crosslinking, so that no sufficient adhesive effect can be accomplished. Moreover, the above alkali-crosslinkable emulsion adhesive shows a marked decrease in alkali crosslinking rate in dry condition, it cannot display a sufficient adhesive power when used in lieu of the adhesive used in the method of Japanese Patent Publication No. 37832/1985 or No. 42828/1985. Thus, the method proposed in the above patent literature comprises coating an adhesive on the surface of a concrete structure and after the adhesive layer has dried, applying a cement-based finish material and if the above emulsion adhesive incapable of alkali crosslinking in dry state is employed in this technique, no adequate adhesive bond strength develops because of insufficient crosslinking, so that no sufficient bond can be established between the concrete structure and the cement-based finish.
Although a variety of methods have been proposed, as mentioned above, for attaining an improved adhesive bond between the concrete-based structure and the cement-based finish layer, there is not known, and a keen demand exists for, a method conducive to safisfactory results in all of heat-resisting bond strength, durability bond strength and atmospheric temperature bond strength and free of the problem of decreased adhesive bond strength in multiple-layer coating.
Accomplished under the situation summarized above, the present invention has as its object to provide a method of finishing a concrete structure which is conducive to improved heat-resisting bond strength, durability bond strength and atmospheric temperature bond strength and free of the problem of decreased bond strength in multiple-layer coating.